Since I am not into the athletic side of fixed gear riding, then most of the extra money I spend on my bike goes to making it look pretty. My bike came with nice Sugino cranks and a good wheelset (Mercier Kilo TT Pro from BikesDirect) already so not much upgrading was necessary. The only non aesthetic change for my bike is the bullhorn handlebar. If you have a lot of money, there is a lot you can do to your bike, sky's the limit obvs ... if you want the flip flop hub, I say go for it. But I don't think you should be worried about a learning curve if you are an experienced cyclist. If anything, I think it would reinforce the habit of coasting and not be beneficial. Maybe the freewheel would be good if you live in a hilly city and need to rest your legs from time to time ... but I've never seen the need on my fixie, frankly.